Upwardly oriented stripping or rectification apparatus

ABSTRACT

Free oil, often an objectionable impurity in synthetic organic detergents, such as sodium lauryl sulfate, is removed from aqueous solutions by extraction thereof with hexane in the presence of lower alkanol, with the proportion of the alkanol present being in a relatively narrow range with respect to the sodium lauryl sulfate, in which range it helps to promote efficient extraction of the free oil by the hexane without solubilizing the hexane in the aqueous medium to such an extent as to result in an extracted detergent containing an unacceptably high proportion of hexane. Separation of the free oil from the aqueous detergent solution is effected in an extractor, to which the hexane is added, in mixture with a minor proportion of lower alkanol, normally isopropanol, and extraction of the free oil takes place after a preliminary mixing of isopropanol with detergent acid or neutralized base in a neutralization vessel and/or in a mixer upstream of the extractor. In a preferred embodiment of the invention the hexane extractant feed to the extractor is that resulting from distillation separation from the free oil of the hexane with some isopropanol. Also, extracted product is evaporated and the evaporator overhead, including isopropanol, hexane and water, is fed to the mixer. The evaporator product is steam stripped, very  preferably in a novel stripper described herein, and the stripper overhead, including isopropanol and water, is conveniently fed to a neutralization vessel in which detergent acid, comprising the product of sulfation of lauryl alcohol with sulfur trioxide (and containing objectionable free oil), is neutralized with aqueous sodium hydroxide. Preferably the deoiling process is a continuous one, with only free oil being removed from the extractor feed, and the hexane and isopropanol are continuously recycled.

This is a divisional, of application Ser. No. 097,520 filed Nov. 6, 1979now U.S. Pat. No. 4,322,367.

This invention relates to the deoiling of synthetic detergents. Moreparticularly, it relates to removal by extraction of undesirable freeoil present in aqueous solutions of synthetic organic detergents,particularly when the detergent is sodium lauryl sulfate and when thefree oil is that resulting from sulfation of lauryl alcohol with sulfurtrioxide, followed by neutralization with sodium hydroxide. However, theinvented process may also be applied to removing free oil from otherdetergent solutions.

Free oil, which usually includes unreacted, partially reacted ordecomposed lipophilic reactant that is employed in the manufacture of asynthetic organic detergent, as well as lipophilic impurities andcontaminants, is usually an objectionable component of such a detergentproduct and therefore, it is often preferred that it be removed. Usuallythe free oil or "ether soluble component" has no desirable detersiveproperties, often lowers detergency, interferes with foaming of theproduct, adversely affects color, odor and taste, and is generallyconsidered to be objectionable in the finished product. Accordingly, ithas usually been specified that the free oil content of a syntheticorganic detergent should be low, being below 1.0 or 1.5% of thedetergent, preferably less than 0.5% thereof and often less than 0.4%thereof, by weight. Although the free oil may be insoluble in water, itis generally emulsifiable or can be solubilized in small quantities, inaqueous detergent solutions. Frequently, it may be solubilized by polarsolvents, e.g., lower alcohols, which may be present in the productsolution. Hence, it is often difficult to remove free oil from suchsolutions. Free oil may be extracted from solid synthetic organicdetergents by a suitable lipophilic extractant or solvent but it isoften more economical to be able to avoid using any special dryingprocess, while making the product from usual aqueous solutions ofdetergent salt, resulting from neutralization of a detergent acid. Yet,when it is attempted to use such lipophilic solvents or extractants toextract aqueous solutions of anionic synthetic organic detergent salts,interfering emulsions and gels may be formed. Having materials presentin the solution to be extracted which aid in preventing suchemulsification and/or gelatin can result in contamination of thedetergent and/or solvent with such materials. If a polar solvent is usedto inhibit emulsification and gelation there can result a cosolventeffect so that objectionable amounts and proportions of free oil andlipophilic solvent or extractant are contained in the aqueousdetergent-containing medium after extraction. In some cases hexane caneven be solubilized in the detergent layer. Also, the employment ofextractants often gives rise to recovery and disposal problems,especially with respect to solvent recovery.

The present invention is of a method of deoiling a synthetic organicdetergent salt, in particular, an anionic detergent, and moreparticularly, sodium lauryl sulfate, by treatment of an aqueous solutionof such salt, containing free oil, with a lipophilic extractant, such ashexane, in such manner as to result in the production of an aqueoussolution of such detergent salt, preferably containing less than 0.5% offree oil on a detergent weight basis. In accordance with the presentinvention a method for deoiling an aqueous solution of sodium laurylsulfate comprises bringing into contact a liquid phase comprising sodiumlauryl sulfate to be deoiled, oil to be removed therefrom, water,isopropanol and hexane, with the proportion of isopropanol: sodiumlauryl sulfate being within the range of 1.3 to 2.5, by weight, and aliquid phase comprising hexane and isopropanol, separating the liquidphases into upper and lower parts, with hexane, isopropanol, free oiland a small amount of water in the upper part and sodium lauryl sulfate,isopropanol, water and hexane in the lower part, separating hexane andisopropanol fom the free oil of the upper part material, preferablyevaporating lower material to remove portions of the isopropanol, hexaneand water therefrom and to increase the concentration of the sodiumlauryl sulfate in the aqueous solution thereof, and stripping alcoholfrom the lower or evaporated solution resulting. The minor amount orproportion of water in the extractor upper part may be a negligibleamount or proportion. It may remain with the free oil residue from thehexane vaporizer or it can go off with the hexane, depending on thevaporizing conditions. Preferably, the deoiling process is a continuousone, the extractant and the evaporator and stripper overheads arerecycled and only make-up extractant, anti-gelling andanti-emulsification solvent, and water, in certain ranges of proportionsof the solvent to detergent, are needed for processing, in addition tothe initial reactants for the manufacture of the sodium lauryl sulfate(which are lauryl alcohol, sulfur trioxide and aqueous solution ofsodium hydroxide). In the mentioned continuous process the contactingand separation of the liquid phases may take place in a conventionalcontinuous countercurrent extractor wherein premixed feed, containinghexane, is added continuously and the recovered hexane-isopropanolextractant is added continuously. The product layer is withdrawncontinuously from the extractor bottom or equivalent location while theextractant is removed from the top or equivalent location. Normally suchremovals are at bottom and top, respectively, but this may be modified,as in centifugal separators, etc. Preferably, the invention relates to acontinuous process but batch adaptations can be made too. Thecombination of extraction, evaporation and stripping operations isimportant to the success of the invention, and the extraction by anextractant that is in substantial equilibrium with the extractedsolution (except for the fatty oil) is also important because it permitsselective removal of the fatty oil without removals of other solutioncomponents, and this makes further processing simpler and moreeffective.

Prior art patents found in a search conducted in the U.S. Patent andTrademark Office include U.S. Pat. Nos. 2,412,916; 2,441,258; 2,615,833;2,655,530; 2,673,207; 2,687,420; 3,365,861;3,941,810; 4,113,438; and4,113,765, which represent the closest prior art known to the inventor.

U.S. Pat. No. 2,412,916 discloses the purification by extraction ofneutralized naphthenic sulfonic acids, wherein the extractant is a lighthydrocarbon material (included among which hexane is mentioned).Isopropanol is present in the aqueous medium, which also contains watersoluble and water insoluble sulfonates, from which unreacted oil isextracted. U.S. Pat. No. 2,441,258 relates to purification of sulfonicacid salts, such as calcium mahogany sulfonate, by treating such a saltwith nitropropane to selectively dissolve mineral oil and otherhydrocarbon matter present, allowing the mixture to settle, andseparating the layers thereof, after which distillations are employed torecover oil-free sulfonate, nitropropane and hydrocarbon oil. U.S. Pat.No. 2,655,530 teaches the neutralizing of an alkylaryl sulfonic acid ina solvent which includes water, alcohol and hydrocarbon, washing thesolution with additional hydrocarbon solvent to remove unsulfonatedalkylaryl hydrocarbon material, and then removing the hydrocarbon,alcohol and water to obtain a concentrated aqueous solution ofneutralized alkylaryl sulfonate. U.S. Pat. No. 2,673,207 describes theneutralization of acid sulfonation products in a two-phase liquidvehicle containing neutralizing agent. One of the phases is an aqueousphase and the other is an organic solvent phase. Among the organicsolvents that are suggested for use are low boiling hydrocarbons. Also,it is mentioned that lower alcohols, such as methyl, ethyl and isopropylalcohols, are preferred for economic reasons and because of theirrelatively low boiling points and inhibiting effects on foams. It isalso suggested that solvent mixtures may be employed. U.S. Pat. No.2,687,420 relates to a process for neutralizing sulfonated organicdetergent acids in an aqueous organic solvent solution, which separatesinto two immiscible liquid phases. Among the organic solvents mentionedare isopropanol but water immiscible solvents are also suggested,providing that they become sufficiently soluble in the aqueous medium.

U.S. Pat. No. 3,865,861 teaches the solvent extraction of unreactedalcohol from an aqueous medium containing sulfated and neutralizedsecondary alcohols, by means of solvent extraction with a waterimmiscible solent, such as petroleum ether. The patent teaches that alow boiling alcohol, such as isopropanol, may be present with theneutralized detergent salt being purified. Unreacted alcohol isseparated from the detergent salt by such solvent extraction andnormally is than freed from the solvent by distillation off of thesolvent, after which the alcohol may be recycled for sulfation. Thepatent also describes stripping off of the solvent alcohol from thedetergent salt and recycling of such alcohol to the neutralizer. U.S.Pat. No. 3,941,810 discloses the sulfonation of aromatic compounds bysulfur trioxide in the presence of a suitable solvent, such as hexane,after which the aqueous sulfonate product resulting, in such solvent, isextracted by a mixture of such solvent and an aromatic compound. Theaqueous sulfonate resulting, removed from the base of an extractioncolumn, is sent to a stripper, where the final traces of solvent andunreacted aromatic substance are removed from it. The small quantitiesof water, solvent and unreacted aromatic reactant removed in thestripper are condensed and recycled. U.S. Pat. No. 4,113,438 mentionspetroleum ether extraction of free oil from water soluble sulfonatedetergents, such as linear alkylbenzene sulfonates and olefinsulfonates. U.S. Pat. No. 4,113,765 describes the use of hexane or otherinert solvent with an alkyl aromatic material being sulfonated by SO₃.However, the hexane is vaporized off from the sulfonic acid product madebefore neutralization thereof and is not employed to extract free oilfrom such detergent acid. The only patent found that is considered to beof any relevance at all to the stripper apparatus, U.S. Pat. No.2,615,833, shows only the use of steam eductors to lift oily materialbeing stripped and thereby carry it upwardly through a bubble traycolumn. In addition to the patents found in the search, it is admittedprior art that free oils have been removed from solid neutralizeddetergents by extraction thereof with ether to determine the percentageof free oil or "ether solubles" present therein.

Although the prior art discloses the purification of aqueous detergentcompositions by extraction of free oil therefrom with lipophilicsolvents, and although the presence of lower alcohols, such asisopropanol, in detergent solutions being extracted, has been taught,the process of the present invention has not been described nor has itbeen suggested and it is not obvious from the references nor from anycombination thereof. For example, the references do not suggest theimportance of the range of proportions of isopropanol:sodium laurylsulfate, the quick separation of liquid phases in the extractor, theevaporation of the lower phase material and the stripping of theevaporated solution resulting nor, more particularly, do they teach theapplication of such processes to the purification of sodium laurylsulfate in a continuous manner and utilizing applicant's novelapparatus, including his stripper.

The invention will be readily understood by reference to the presentspecification and the accompanying drawing in which:

FIG. 1 is a schematic flow diagram illustrating deoiling of a particulardetergent, sodium lauryl sulfate, and showing the manufacture of suchdetergent and the recycling of recovered material to the deoiling andmanufacturing processes; and

FIG. 2 is a partially centrally sectioned elevation of a novel strippingcolumn for use in the described deoiling process, for removal of alcohol(and water) from the deoiled detergent solution.

In FIG. 1 a known method for the manufacture of neutralized detergentcontaining free oil is shown on the left side of separating line 11 andthe deoiling of such detergent and the recoveries and recyclings ofvarious materials resulting from the manufacturing and deoilingoperations are shown on the right side thereof. Lauryl alcohol andsulfur trioxide gas (which may be pre-blended with diluent gas, such asair or nitrogen) are fed to reactor 13, via lines 15 and 17,respectively, sulfation takes place, and the sulfuric acid esterresulting, unreacted sulfur trioxide present, and free oil are removedfrom the reactor and are passed via line 19 to neutralizer 21, to whichan aqueous solution of sodium hydroxide is added through line 23, wateris added via line 25 and recovered stripper overhead, comprisingisopropanol and water, is added via line 27. The neutralized base,including sodium lauryl sulfate, free oil, sodium sulfate, isopropanoland water, is passed via line 28 to a mixer 29, in which it is mixedwith recovered evaporator overhead, comprising isopropanol, hexane andwater, which overhead is fed to the mixer via line 31. The mixture ofmaterials resulting, including sodium lauryl sulfate, free oil, sodiumsulfate, isopropanol, hexane and water, is fed through line 33 toextractor 35, to which recovered hexane, with isopropanol, is fed fromhexane vaporizer 37 through line 39. In the extractor the feed mixtureand recovered hexane extractant material are brought into intimatecontact with each other, the feed, for the most part falling, and theextractant rising, so that the fatty oil is extracted by the upwardlymoving extractant liquid. The lower, hydrophilic layer of extractedproduct resulting, including sodium lauryl sulfate, a minor proportionof the free oil charged to the extractor, sodium sulfate, isopropanol,hexane and water, is removed via line 41 and is fed to evaporator 43,and the upper lipophilic layer, comprising hexane, isopropanol and amajor proporton of the free oil that had been charged to the extractor(often plus a small, sometimes negligible proportion or amount ofwater), is removed and sent through line 45 to the hexane vaporizer.From such vaporizer (or hexane recovery unit), which is maintained at anelevated temperature, e.g., 65°-85° C., hexane and isopropanol areremoved overhead and condensed, and subsequently pass through line 39 tothe extractor, and the free oil is taken off through line 47. The freeoil may be recycled back to reactor 13 with the lauryl alcohol reactantcharged, if desired, but such recycling is not normally practicedbecause of the usual objectionably dark color of the free oil and itsvariable content of lauryl alcohol. From evaporator 43, which is awiped-film type of evaporator to prevent poor heat transfer to thesolution being evaporated due to gel formation at higher detergentconcentrations thereof, and which operates under vacuum, the mixture ofisopropanol, hexane and water previously mentioned is taken off and sentto mixer 29 through line 31, while the evaporator product, comprisingsodium lauryl sulfate, a small proportion of free oil, sodium sulfate,isopropanol, and water, is removed through line 49 and is fed tostripper 51, which is operated under vacuum and at a temperature whichmay be slightly higher than that of the evaporator. The evaporator is ofthe wiped-film type because otherwise the heat transfer surface willbecome blocked with gel and will be inactive, which can causedegradation of the detergent and inoperativeness of the evaporator.Usually the evaporation product contains practically n hexane, but asmall proportion, e.g., 0.1 to 0.3%, may be present. Steam is admittedto stripper 51 through line 53 and the overhead from the stripper,isopropanol and water in mixture, is sent to neutralizer 21 through line27, as previously described. The product, comprising sodium laurylsulfate, a very small percentage of remaining free oil, sodium sulfateand water, is removed through line 55. Additional water, for finalconcentration control, mixes with the product in line 55, being fed tosuch line through line 57.

In FIG. 2 is shown the construction of a novel stripping column for usein the process of the present invention to separate lower alkanol(isopropanol) from synthetic detergent (sodium lauryl sulfate),inorganic salt (sodium sulfate), water and the small proportion ofunextracted free oil remaining. The present stripper, which may beutilized for other separations, too, is especially advantageous in theprocess of this invention because it separates solvent from aqueousdetergent solution without the virtually insurmountable foaming problemswhich are otherwise often encountered in making such separations. Thiscolumn is unique in that it permits foaming solutions to be rectified ina continuous, countercurrent manner, which up to now has beenimpossible.

Numeral 61 represents the stripping column, which comprises acylindrical wall portion 63, internal agitation (foam-breaking) means 65(which is not always required), drive means 67, connecting means 69,between the drive and agitation means, upper sealing means 71, lowersealing means 73, separators 75, for separating the column intosections, vapor-liquid contacting lines 77, liquid lines 79,vapor-liquid mixing means 81, entrances 83 for additions of vapor-liquidmixtures to the column, exits 85 for vapor leaving the column, exits 87for liquid leaving the column, steam or stripping gas inlet 89, vaporoutlet 91, feed inlet 93 and product outlet 95. Numeral 97 designateswhat may be characterized as a liquid-vapor contacting zone and aliquid-vapor separating one is represented by numeral 99. Paths of vaporand liquid are designated respectively by numerals 101 and 103.

In column 61, which may be of a single piece, with inlets and outletsprovided thereon, or may be of a plurality of component parts, fastenedtogether, elements 105 can be provided in each column section, if deemeddesirable, as a part of internal agitation means 65, between columnseparating members 75. As illustrated, internal agitation means 65 arepaddles 105, shown as a blade form, affixed to rotatable shaft 107,which shaft is mounted in bearings 109 and 111. As shown in the drawing,such bearings are associated with column separators 75, which includesealing gaskets 113 around the peripheral portions thereof.

In the mixing portion of the apparatus, wherein steam or vapor mixtureis brought into intimate contact with liquid from which lower alkanol,e.g., isopropanol, is being separated by vaporization, such contact maybe effected due to the Venturi nature of the mixing tee 81, notillustrated, and in the connecting piping 77, which, to obtain bettermixing effects, may be at least partially packed with any of varioussuitable types of packing, e.g., corrugated metal strips. To preventunintentional back-feeding of liquid, which might possibly occur due tomomentary steam pressure increases, check valves, such as thatillustrated at 115, will preferably be installed, thereby preventingback-feeding of the liquid and bypassing by it of the vapor. In theillustration the U-tube shaped legs of the side passages help to prevent"blow-by" of steam or vapor but the use of check valves is more positiveand is of further assistance. At the column bottom a U-shaped line orequivalent means is provided, not shown, to maintain liquid in thecolumn or drain line 95, so as to prevent steam or vapor escape throughthat line.

In operation, the present stripping apparatus, normally covered withinsulating material (not shown) around the various parts thereof so asto minimize heat losses, is fed at 89 with steam at the desiredtemperature, pressure and rate, which steam (and later,steam-isopropanol mixture) passes through outlet 91 to a condenser, notshown, and addition of the feed, comprising detergent, inorganic saltlower alkanol, water and a small proportion of free oil, is commencedthrough inlet 93. The path of the vapors up the column is apparent fromthe drawing and it is seen that vapor will mix with the feed in themixing or Venturi tees and will carry the liquid feed upwardly throughthe side pipings back into the column, where paddles or beaters 105 willhelp to separate any foam resulting into liquid and vapor phases. (Itwill be evident that the numerals for the various parts of the inventionrelate to each of the replications of such parts in the column). Then, avapor, enriched in isopropanol as a result of the mass transferoccurring in the liquid-vapor contacting zone, will pass out exit 91 tothe condenser, for condensation to liquid. Also the liquid, from whichsome isopropanol has been removed, will travel downwardly through line79 until it fills the U-shaped portion thereof. Again, but this time ina lower portion of the column, the mixture of liquid and vapor will beseparated into liquid and vapor phases, the vapor will move upwardly andthe liquid will move downwardly, and the operations will be repeated. Ineach stage as the liquid moves downwardly through the column, it hasisopropanol removed from it by a vapor which is leaner in itsequilibrium isopropanol content as the bottom of the column isapproached. Correspondingly, as the feed descends through the column itwill lose isopropanol, so that when it is withdrawn from the stripperthe isopropanol content will be essentially nil.

The materials of construction of the stripping column will preferably benon-corrosive, such as stainless steel, glass or plastic, e.g.,fiberglass reinforced polyester resin. However, other suitable materialsmay also be employed, including ceramics, steels, aluminum, other metalsand alloys, phenol-formaldehyde resins, nylons, polypropylene,polyethylene, neoprene, polyurethane, polytetrafluoroethylene, etc.,depending on the function to be performd by a particular part. So as toprovide for visual observation of the effectiveness of the foam-breakingor agitating means, sight glasses may be provided in the column wall.Instead of using paddles or beaters for breaking foam, other means maybe employed, including centrifugal or cyclone separators, internallylocated (within the stripping column) or externally positioned. Thepiping, illustrated externally of the column in FIG. 2, may be relocatedinternally thereof and such relocation is especially convenient andpracticable when internal centrifugal separators or equivalent devicesare employed to break the foam.

An important feature of the present invention is that the steam or vaporwill be brought into intimate contact with the liquid from which avolatile component is being vaporized and removed, and that after beingbrought into such intimate contact the vapor and liquid are separated,with the vapor continuing to pass onwardly (upwardly) into a series ofother contact and separation areas, whereas the liquid passes in anopposite direction (downwardly), after separation from the entrainingvapor, to where it is contacted by upwardly moving vapor andsubsequently is directed to a lower (than the previous) separating zone,from which it then continues to move downwardly. The upward movement ofvapor and the downward movement of liquid being stripped superficiallyresemble conventional distillation and stripping column operations, withrespect to component movements, but because such apparatuses usuallyemploy bubble caps or other means for providing liquid levels on platesand for bringing liquids and gases into contact, they often createobjectionable foaming and additionally, are often not as efficient inbringing the contacting liquid and vapor phases into equilibrium in theshort contact periods of the column operations. The present apparatusovercomes these difficulties and disadvantages. In this apparatus, forexample, vapor speeds of about 10 to 200 meters/second, preferably 20 to150 m./sec., e.g., 30 m./sec., are practicable, with good efficienciesin reaching equilibrium between liquid and vapor, and efficientseparation of the liquid and vapor. In the event that the separation isnot adequate with five column sections, such as illustrated, the numberthereof may be increased and it is contemplated that as many as ahundred such sections can be employed, although normally the numberthereof will be from 3 to 30, preferably being from 4 to 20. Of course,column size may be adjusted, as desired, but normally the columndiameter will be from 0.1 to 3 m., preferably 0.2 to 1.5 m. and thecolumn section length will be from 0.1 to 1 m., preferably from 0.1 to0.5 m. The column cross-sectional shape will preferably be circular butother shapes, e.g., square, rectangular, hexagonal and elliptical, maybe used, and may be particularly advantageous to provide room forinternal mixers, separators and passageways.

The detergent material being purified by the method of this invention,as described herein, is very preferably sodium lauryl sulfate in anaqueous medium containing water and free oil. Other materials may bepresent with the active detersive ingredient (A.I.), such as sodiumsulfate and polar solvent, such as lower alcohol, e.g., isopropanol.Such aqueous solutions will normally contain from 25 to 33%, preferablyfrom 28 to 32%, and most preferably 30 to 32% of sodium lauryl sulfate;1.0 to 6%, usually 1.0 to 4% and frequently 1.2 to 3% of free oil, 0.3to 3%, usually 0.4 to 2.5% and frequently 0.5 to 2% of sodium sulfate; 0to 10%, usually 0.1 to 8% and often 1 to 5% of lower alkanol, e.g.,isopropanol; and 50 to 75%, usually 55 to 70% and typically 60 to 67% ofwater. On a detergent A.I. basis the ranges of proportions are 3.2 to19.4, 3.2 to 12.9 and 3.9 to 9.7 percent or parts per hundred for thefree oil; 1 to 9.7, 1.3 to 8.1 and 1.6 to 6.5 for the sodium sulfate;and 0 to 32.2, 0.3 to 25.8 and 3.2 to 16.1 for the lower alkanol. Theneutralized base may also contain other materials normally present indetergent compositions but preferably the contents thereof will beminimized, normally being limited to 10%, preferably 5% and mostpreferably 1%, on dry basis. Of course, when other detergents are beingdeoiled their initial and final oil contents may differ from those givenabove, and even with the higher alcohol sulfates being purified, oilcontents outside the ranges given may be encountered and may result.

Although the neutralized base to be deoiled may best be made with a lowcontent of inorganic salt and free oil by sulfation of lauryl alcoholwith gaseous sulfur trioxide and subsequent neutralization in an aqueousmedium with aqueous sodium hydroxide solution (often of 5 to 15% NaOHcontent therein), and often in the presence of a desired quantity, suchas that previously described, of isopropanol or other suitable lowermolecular weight polar solvent (which may help to prevent gelling andexcess foaming), other manufacturing methods may also be utilized whichresult in comparable aqueous solutions or similar aqueous media of suchconcentrations of components as were mentioned previously. Thus, aneutralized base product of oleum or sulfuric acid sulfation of laurylalcohol may also be employed. Furthermore, although the proportions ofvarious components of the neutralized base and extractant materials, andthe conditions of the present invention, are important with respect tothe manufacture of desired deoiled sodium lauryl sulfate product, suchconcentrations, proportions and conditions, sometimes with minorvariations, may also be useful in the manufacture of correspondinghigher fatty alcohol sulfates, such as those wherein the higher fattyalcohol sulfate is of 10 to 18 carbon atoms, e.g., 12 to 16 carbonatoms, or is a mixture of alcohols of such type, e.g., those obtainedfrom coconut oil and other nut, seed or kernel sources. Also, thedeoiling method described may be successfully applied to removingunwanted free oil from other synthetic organic detergents, but isespecially useful for purifying the anionic detergents, such as higherfatty monoglyceride sulfates and sulfonates, higher fatty alcoholpolyethoxy sulfates, linear higher alkylbenzene sulfonates, alkylsulfonates, olefin sulfonates and paraffin sulfonates. With respect tosuch detergents and the preferred fatty alcohol sulfates, while thesodium salts thereof are normally utilized, other salts may also bepurified by the method of this invention, including those of otheralkali metals, such as potassium, water soluble salts of alkaline earthmetals and magnesium, ammonium salts and alkanolamine salts, such astriethanolamine salts. Usually the anionic detergents will include alinear alkyl of 8 to 20 carbon atoms, preferably a higher alkyl of 12 to18 carbon atoms. For example, the following detergents may also bedeoiled by methods substantially like those described herein for thepreferred sodium lauryl sulfate: sodium linear dodecyl benzenesulfonate; sodium linear tridecyl benzene sulfonate; sodium hydrogenatedcoconut oil fatty acids monoglyceride sulfate; sodium laurylmonoglyceride sulfonate; sodium ethoxylated lauryl alcohol sulfate (3mols ethylene oxide per mol); sodium ethoxylated lauryl alcohol sulfate(2 mols ethylene oxide per mol); sodium alpha-olefin sulfonate (12-18carbon atom content olefin); sodium alpha-olefin sulfonate (12-14 carbonatom content olefin); sodium alpha-olefin sulfonate (16-18 carbon atomcontent olefin); and secondary higher alcohol sulfates.

The lipophilic solvent, while preferably hexane, may also be otheralkanes, e.g., pentane, heptane and mixtures of such materials, usuallypreferably being linear alkanes of 4 to 9 carbon atoms, but otherhydrocarbons and equivalent lipophilic solvents may also be employed.Desirably, such materials will have normal boiling points in the rangeof 50° to 75° C., preferably 65° to 70° C. However, by adjustment ofdistillation, evaporation, stripping and extraction conditions, one mayemploy other solvents, having other boiling points and ranges, and mayutilize appropriate mixtures thereof.

The polar solvent employed is very preferably isopropanol but otherlower alkanols, such as methanol and ethanol, may also be used, as maybe equivalent hydrophilic solvent materials capable of inhibitingemulsification and/or gelation of the detergent and the lipophilicsolvent under the processing conditions employed. Hereafter, forsimplicity, reference will be to the prevention of gelation but it is tobe understood that such reference is meant to relate to prevention ofemulsification, too, with gelation prevention and without. The waterused will preferably be deionized water, to avoid any interferingreactions of impurities in the water with the detergent and othermaterials which may be present, but ordinary tap water may also be used,depending largely upon the purity of the final product desired.

By following the method of this invention there may be produced anaqueous solution of the desired detergent salt wherein the free oilcontent has been reduced to less than 1%, preferably less than 0.5% andmore preferably, less than 0.4%, e.g., to 0.3% or less, on a detergentA.I. basis, and in some cases the final free oil content may be almostnil. Such is often important in producing satisfactory productsincorporating the particular detergent. Thus, the presence of free oilmay otherwise have a destabilizing effect on perfumes and colors ofproducts, can inhibit foaming, can make products undesirably pasty and,in liquid products, can cause separations of oily layers from theproducts. When synthetic organic detergents other than sodium higherfatty alcohol sulfate are purified of free oil, which oil usuallycontaminates such detergents as a result of manufacturing processes,corresponding diminutions of oil contents are also obtainable and areadvantageous. On an A.I. (active ingredient or detergent solids) basis,the sodium sulfate content of the deoiled product will usually be in therange of 0.5 to 5%, often being from 1 to 3% and typically being from 1to 2%. The A.I. concentration in the aqueous solution of product willusually be from 25 to 35%, preferably 27 to 33%, and typically 28.5 to31.5%, e.g., 30%, but it can vary, too. Normally, it will be aconcentration at which gel is not formed.

In practicing the method, the neutralized base, containing free oil, ischarged to a mixer, wherein it is mixed with the recovered hexane,isopropanol and water from the evaporation stage at a suitabletemperature, usually in the range of about 15° to 70° C. preferably from30° to 55° C., more preferably 35° to 45° C. and most preferably about40° C., at atmospheric pressure (or 0.9 to 1.1 atmosphere) for a timelong enough to result in intimate mixing of the base and the solventmix, so that a single phase results. Such mixing time, is not critical,but is usually in the 1 to 10 minute range.

The extractor will normally be operated at the mentioned temperaturesand at a pressure of 0.9 to 1.1 atmosphere, preferably at atmosphericpressure. The feeds to the extractor will be within the temperatureranges described for the mixer, which, in some instances, may involvepreliminary temperature adjustments of feed components. In continuousextraction, all that is needed is for the contact time between the twophases in the extractor to be sufficient for adequate transfer of thefree oil from the detergent solution to the extractant. Such time willusually be within the 1 to 10 minute range but more or less time forholdup in the extractor may be taken. In the extraction the feed may bein dispersed form at the top and drops of it may fall through theextractor, intimately contacting the solvent phase but without any ofthe feed except the free oil dissolving in it. In other words, the twoliquid phases remain immiscible so the hexane and alcohol do nottransfer between the phases but the phases are in close contact in theextractor so that the free oil can and does pass to thehexane-isopropanol phase. While continuous operations are highlypreferred the operations may be carried out batchwise, too.

The upper liquid phase removed from the extractor will usually comprisefrom 85 to 99%, preferably 90 to 96% of hexane, 2 to 15%, preferably 4to 8% of isopropanol, and the maximum free oil content compatible withproducing the desired deoiled product. Often such oil content can be 0.1to 1%, preferably 0.2 to 0.5%. Water content, if any, can be 0 to 1%,preferably 0 to 0.2%. The product removed from the base of theextractor, which usually will weigh from 35 to 65%, preferably 45 to 55%of the weight of the upper body discharged from the extractor, willusually comprise from 10 to 20% of A.I., preferably 14 to 18% thereof,0.0 to 0.2% of free oil, preferably 0.02 to 0.1% thereof, 0.0 to 0.5% ofNa₂ SO₄, preferably 0.1 to 0.3% thereof, 15 to 40% of isopropanol,preferably 20 to 30% thereof, 5 to 25% of hexane, preferably 10 to 20%thereof, and 30 to 50% of water, preferably 40 to 45% thereof. Withinthe ranges given it is considered important for best results that theratio of isopropanol:A.I. in the detergent solution to be deoiled shouldbe in the range of about 1.3 to 2.5, preferably 1.3 to 2, e.g., about1.5. Such will also be the ratio of these components in the extractedproduct when the process is operating at peak performance.

The upper lipophilic phase from the extractor is passed in its entiretyto a hexane vaporizer operating at atmospheric pressure (or at apressure in the 0.9 to 1.1 atmosphere range, although greater vacuumsare sometimes desirable, e.g., to 0.1 or 0.2 atmosphere absolute), andat a temperature in the range of 65° to 90° C., preferably 70° to 80°C., e.g., 75° C., and the free oil is separated from the hexane andisopropanol charged, with the free oil being removed almost completelyor completely from the bottom of the vaporizer and with the hexane,isopropanol and a small amount of water (in some cases) being removedfrom the top thereof. The hexane-alcohol mix removed is of a very highpurity, containing less than 0.1% of free oil, on a weight basis,preferably less than 0.05% of free oil and most preferably 0.04% or lessof such oil. Holdup time in the hexane vaporizer will usually be from0.1 to 30 minutes, preferably 0.5 to 10 minutes and more preferably,about 1 to 5 minutes.

The deoiled extractor product is passed into an evaporator of the wipedfilm type, wherein the material to be evaporated passes through anarrow, preferably peripheral, passageway in contact or operativerelationship with heat transfer means. To prevent any buildup of gel orother deposit in such passageway or on such heat transfer means thesurfaces thereof are continually wiped by passing wiping means over them(and often in contact with them). In the evaporator the temperature willusually be in the range of 25° to 100° C. preferably 60° to 75° C., butthe temperature used depends upon the stability of the detergent beingprocessed. The pressure will usually be in the range of 150 to 350 torr,preferably 200 to 300 torr. Holdup time in the evaporator will generallybe from 0.01 to 20 minutes, preferably 0.02 to 1 minute and morepreferably 0.02 to 0.2 minute. The evaporator overhead removed willnormally include from 40 to 60% of isopropanol, 20 to 40% of hexane and10 to 30% of water, with such proportions preferably being 45 to 55% ofisopropanol, 25 to 35% of hexane and 15 to 25% of water. The evaporatorproduct removed may contain from 25 to 40% of A.I., preferably 27 to 37%and more preferably 30 to 34% thereof, and the percentage of free oilwill be from 0.0 to 0.5%, preferably being from 0.0 to 0.3% and morepreferably from 0.0 to 0.2%, e.g., 0.1%. Isopropanol content willnormally be from 1 to 10%, preferably 1 to 5% and more preferably 2 to4%, and hexane content will usually be in the range of 0.0 to 0.5%,preferably 0.0 to 0.2% and more preferably 0.0 to 0.1%. The waterpresent will usually be from 50 to 80%, preferably 60 to 70% and morepreferably 62 to 66%. The proportion of evaporator overhead toevaporator product taken off will normally be from 0.7 to 1.5,preferably 0.9 to 1.2, more preferably 0.9 to 1.1, e.g., about 1. Thesefigures, and others given above, are for sodium lauryl sulfatepurification from free oil and can vary when other detergents areprocessed.

In the stripper the temperature and pressure will be held about the sameas those in the evaporator, from which the evaporator product is fed tothe stripper, but the stripper temperature may be slightly higher, e.g.,1°-10° C. or 2°-5° C. higher. For stripping, the only material chargedto the stripper, in addition to the charge to be stripped, is steam, andthe proportion thereof is about 15 to 30% of the total weight of watercharged to the stripper in the solution to be purified, preferably being20 to 25% thereof. Usually one weight of steam is enough to vaporizethree weights of lower alkanol, so if allowances are made for heatlosses in the equipment, and if one knows the alkanol content of thesolution to be stripped, the minimum steam charge can be calculatedeasily. However, usually an excess is employed, with the proportion ofsteam charged to isopropanol to be removed being in the range of about4:1 to 10:1, preferably 4:1 to 6:1, e.g., 5:1. The stripper overheadcomprises from 10 to 30% of isopropanol and 90 to 70% of water,preferably 15 to 30% and 85 to 70%, respectively. To the strippedproduct removed there is added additional water for accurate control offinal product composition, with the proportion of water in such productbeing 60 to 80%, preferably 65 to 75%, the proportion of A.I. being 20to 40%, preferably 25 to 35%, the proportion of sodium sulfate being 0to 10%, preferably 0 to 1% and the proportion of free oil being from 0to 0.2%, preferably 0 to 0.1%. Such concentration will be chosen toavoid gelation.

Of course, while the described operation proportions are preferred, theymay be varied, providing that the process effected is essentially thesame. Also, some variations may be made between "batch" and continuousprocesses and when different detergents are being deoiled. However, itis important to utilize only enough of the anti-emulsification andanti-gelling agent (isopropanol, in a preferred case) as needed, so asto prevent any excess amount thereof from helping to solubilize thelipophilic solvent and the lipophilic free oil, which would makedeoiling of the detergent more difficult. Variations may also be made inthe processing conditions, e.g., temperatures, pressures, times, mixingtechniques, while still operating within the invented method.

The following example illustrates but does not limit the invention.Unless otherwise indicated, all parts are by weight and all temperaturesare in degrees Centigrade throughout this specification.

EXAMPLE

A neutralized detergent base, consisting of 31.6% of sodium laurylsulfate (A.I.), 1.3% of free oil (higher fatty alcohol, etc.), 0.5% ofNa₂ SO₄, 3.4% of isopropanol and 63.2% of water, is made by reacting 525parts of lauryl alcohol and 207 parts of sulfur trioxide in a reactor,according to a known method, to produce 695 parts of the desiredsulfuric acid ester, 30 parts of free oil and 7 parts of sulfurtrioxide, and then neutralizing such acid mix with 1,639.4 parts ofdilute sodium hydroxide solution, containing 107 parts of sodiumhydroxide, 1,452.4 parts of water and 80 parts of isopropanol. 320 Partsof the water and the isopropanol came from stripper overhead, which wasreturned to the neutralizer. During the neutralization reactions 12parts of sodium sulfate are formed, plus 46.7 parts of water. Thus, theneutralized base mixture removed from the neutralizer contains 750 partsof sodium lauryl sulfate, 30 parts of free oil, 12 parts of sodiumsulfate, 80 parts of isopropanol and 1,499 parts of water, making atotal of 2,371 parts.

The 2,371 parts of base mixture, the free oil content of which is to bediminished so as to make the product satisfactory for use as detergentcomponent of a dental cream product, are added, at a temperature of 45°C. to a mixer, to which evaporator overhead consisting of 1,070 parts ofisopropanol, 690 parts of hexene and 496 parts of water, is added, andmixing is commenced and continued for about five minutes. After thoroughmixing of the neutralized base and evaporator overhead, so that a singlephase is produced, 4,627 parts thereof are continuously added at about40° C. to an upper portion of a conventional extractor, and 9,000 partsof a recovered hexane-isopropanol mixture (94% hexane and 6%isopropanol), including 8,460 parts of hexane and 540 parts ofisopropanol, are added at 40° C. to the extractor at a lower portion.The extractor is maintained at about atmospheric pressure and thelighter solvent phase, immiscible with the aqueous phase, rises throughthe extractor as a continuous phase and is withdrawn at an upper portionthereof, while the heavier, aqueous phase, initially converted todroplet form, falls through the extractor and is removed at the bottomthereof as a continuous phase, essentially free of oil. The solventphase removed at the top of the extractor contains 8,460 parts ofhexane, 540 parts of isopropanol and 27 parts of free oil. This mixture,at 40° C., is fed to a hexane vaporizer, at atmospheric pressure and ata temperature of 80° C., and a 94% hexane content hexane-isopropanoldistillate is removed at the top of the vaporizer (a negligibleproportion of water may also be present), is cooled and is returned tothe extractor, as previously mentioned. 27 Parts of free oil are removedfrom the bottom of the vaporizer. Although such free oil may berecycled, usually it is disposed of as waste, largely because of itsobjectionable color and odor, which make it an undesirable component formany products and an undesirable reactant to produce products intendedfor ingestion or personal use.

The extractor product, from which a significant proportion of free oilhas been removed, which product includes 750 parts of A.I., 3 parts offree oil, 12 parts of sodium sulfate, 1,150 parts of isopropanol, 690parts of hexane and 1,995 parts of water, making a total of 4,600 parts,is next subjected to evaporation to remove solvents therefrom and toconcentrate it. In the wiped film evaporator used, operated at atemperature of 60° C. and a pressure of 250 torr, with a residence timeof about two seconds, 4,600 parts of extractor product are reduced to2,344 parts of evaporator product, with 2,256 parts of evaporatoroverhead of the type previously described. The evaporator productconsists of 750 parts of A.I., 3 parts of free oil, 12 parts of Na₂ SO₄,80 parts of isopropanol and 1,499 parts of water. This evaporatorproduct is subsequently stripped of isopropanol (along with some of itswater content) in a stripper of the type illustrated in FIG. 2. Thestripper is operated at an absolute pressure of 250 torr and atemperature of 60° to 70° C., with the residence time in the stripper ofthe evaporator product being about five minutes during its descent fromthe top to the bottom of the stripper column. In addition to theevaporator product charged, steam is charged to the stripper at thebottom thereof at the rate of about 400 parts per 2,344 parts ofevaporator product. At the top of the column the remaining strippingsteam and isopropanol vapor with it are condensed and are then returnedto the neutralizer, as previously described. At the bottom of the columnthe product is taken off at a temperature of about 70° C. and about 156parts of water are blended with it, so as to result in a final productof desired A.I. content, consisting of 750 parts (30%) of A.I., 3 parts(0.1%) of free oil, 12 parts (0.5% of Na₂ SO₄, and 1735 parts (69.4%) ofwater.

During operation of the stripper, if excessive foam is noted in thesight glasses, the paddles operate and break it down, and goodseparation of isopropanol from the evaporator product charged to thestripper is obtained. The concentrations of A.I. for processing arechosen so as to be below the gelation range thereof, while yet beingsubstantially high. Of course, variations in the proportions of A.I. andwater are possible, free oil purifications to different extents may beobtained and other modifications of the method may be made, within thisinvention.

The deoiling operation described is utilized continuously for severalruns over multi-hour periods, and it is considered that on the basis ofthe experience obtained in these runs, it may be employed indefinitely.

In addition to deoiling sodium lauryl sulfate, the described method mayalso be employed with other higher alcohol sulfates, including sodiumcetyl sulfate, sodium palmityl sulfate and potassium lauryl sulfate. Ofcourse, in these cases and when processing other synthetic organicdetergents, temperatures, pressures, proportions, times and othervariables will be suitably regulated for best purifications.

In addition to removing free oil from the higher fatty alcohol sulfates,the described process has also been employed to diminish the free oilcontents of other anionic detergents in aqueous solution, including:sodium linear dodecyl benzene sulfonate; sodium linear tridecyl benzenesulfonate; sodium hydrogenated coconut oil fatty acids monoglyceridesulfate; sodium ethoxylated lauryl alcohol sulfate (3 mols ethyleneoxide per mol); sodium ethoxylated lauryl alcohol sulfate (2 molsethylene oxide per mol); sodium ethoxylated lauryl alcohol sulfate (1mol ethylene oxide per mol); sodium alpha-olefin sulfonate (12-18 carbonatom content olefin) sodium alpha-olefin sulfonate (12-14 carbon atomcontent olefin); and sodium alpha-olefin sulfonate (16-18 carbon atomcontent olefin). Free oil contents of all were significantly reducedbut, because the monoglyceride sulfate was initially considerably higherin free oil content, comparable purification thereof was obtainable withtwo passes through the extractor.

Although the invention has been described with respect to preferredembodiments and illustrations thereof, various modifications therein maybe made without departing from it. For example, instead of utilizingnormal gravitational forces to promote separation of the extractorlayers, centrifugal separations may be employed, and extractionconditions may be changed. Similarly, various combinations oftemperature and pressure may be utilized to promote vaporization,evaporation and stripping. Different desired final concentrations ofmaterials are also obtainable by procedural changes in the describedmethod. Yet, despite all such variations in the method, and despitedeoilings of various detergents, the method and apparatus operateefficiently, allowing the purification of the detergents withoutunacceptable losses of product, in a closed system from which solventsemployed do not escape to cause air pollution and other problems, and inwhich system the various solvents are reused continuously. The methodmay be employed for removing free oil from aqueous detergent solutionscontaining larger proportions of inorganic salt and is also useful forthe purification of detergents that are essentially free of such salts.Of course, if too much inorganic salt, e.g., sodium sulfate, is presentin the aqueous detergent solution being purified of free oil it may bethrown out of solution when it is brought into contact with theisopropanol in the mixer and in the extracting medium. This could bebothersome in subsequent operations and could result in a product of toohigh a salt content. Therefore, it may be desirable, when such an excessof inorganic salt is present, to separate at least some of it outinitially, as by isopropanol treatment and filtration or settling,before carrying out the extracting, vaporizing, evaporating andstripping steps of this invention.

In another modification of the process of this invention, the portion ofextracted material from the lower part of the extractor may be feddirectly to the stripper, rather than to an intervening evaporator,although the use of the evaporator is highly preferred. In suchoperation, the stripper overhead may be recycled back to the mixer, towhich the evaporator overhead would otherwise have been sent, or aportion of the stripper overhead, e.g., 25 to 75%, may be sent to theneutralizer, with the remainder thereof being sent to the mixer. Inother variations of the invention recyclings of removed materials,including lipophilic and hydrophilic solvents, may be modified. Forexample, when employing the evaporator the stripper overhead may berecycled at least in part to the mixer or other suitable apparatus priorto stripping, instead of all of it being sent to the neutralizer.

The stripping apparatus described may be utilized for other strippingoperations involving detergent solutions or may be employed forstripping of materials other than detergents, being especially usefulwhen the materials tend to foam during distillation, rectification,stripping and similar processing operations. The stripping apparatus ofthis invention is also useful for stripping volatilizable materials fromnon-foaming compositions because it allows high speed movement of thestripping gas and vapor, e.g., steam plus volatilized solvent, throughthe stripper without objectionable entrainment, which is otherwise oftenencountered. In other words, the foam breaking means of the presentstripping apparatus and the flow patterns in the apparatus, whileexceedingly useful for preventing objectionable foaming and foamentrainment in the stripping gas, is also useful for preventingundesirable non-foam droplet or other entrainment of material in thestripping medium. For example, the present stripper may be employed forstripping volatiles from petroleum oils and use of the stripper allowshigher throughputs than are obtainable with conventional bubble trayunits.

The invention has been described with respect to various embodiments,including two illustrations and an example of different aspects thereof,but is not to be limited to these because it is evident that one ofskill in the art, with the present teaching before him, will be able toutilize substitutes and equivalents without departing from theinvention.

What is claimed is:
 1. An upwardly oriented stripping of rectificationapparatus, adapted for stripping vaporizable material from liquids,which comprises a plurality of sequentially adjacent and interconnectedchambers, with terminal chambers at upper and lower ends thereof; eachof the chambers including an outlet near the bottom thereof for removalfrom the chamber of the liquid being rectified; an inlet above the saidoutlet for admission to the chamber of a liquid-vapor mixture; an outletabove said inlet for excursion from the chamber of vapor; a firstconnecting walled passageway extending between the vapor outlet of thelower adjoining chamber and the said liquid-vapor inlet; a secondconnecting walled passageway extending between the liquid outlet of thehigher adjoining chamber and an inlet to the said first connectingpassageway, with the proviso that the first passageway in the lowerterminal chamber extends between a steam or stripping gas inlet and thesaid vapor-liquid inlet of the said lower terminal chamber and thesecond passageway is not present in the upper terminal chamber; meansfor introducing feed to the stripping apparatus near the upper endthereof; means for adding steam or other stripping gas to said strippinggas inlet; and means for withdrawing stripping gas or steam and materialstripped from the feed, in gaseous or vapor form, near the upper end ofthe apparatus.
 2. A stripping apparatus according to claim 1 wherein thesecond connecting passageways include means for preventing flow ofmaterial from the first connecting passageways to the second connectingpassageways except through the chambers.
 3. An apparatus according toclaim 1 wherein the first and second passageways are located exteriorlyof the chambers.
 4. Apparatus as claimed in claim 3 in which the inletat which the second connecting passageway connects with the firstconnecting passageway is adjacent to the vapor outlet of the loweradjoining chamber.
 5. Apparatus as claimed in claim 4 in which thesecond passageway includes a U-tube portion the arms of which extendupwardly, the bottom of the U-tube being below the inlet to the firstpassageway.
 6. A stripping apparatus according to claim 5 wherein saidflow preventing means include check valves in the U-shaped portions ofthe second passageways.
 7. An apparatus according to claim 1 whichincludes means for breaking foam in at least some of the chambers. 8.Apparatus as claimed in claim 7 in which said means for breaking foamare located in each chamber.
 9. An apparatus according to claim 8wherein the foam breaking means include paddles or beaters which aredriven off a single shaft which extends through the plurality ofassembled chambers, said shaft being sealed where it passes throughchamber walls so as to prevent direct chamber-to-chamber flow ofmaterial through such walls.
 10. An apparatus according to claim 1wherein the number of chambers is from 3 to 100, with all beingessentially the same except the terminal chambers, and wherein theconnecting passageways between different chambers are of the same firstand second types.
 11. In an upwardly oriented stripping or rectificationapparatus, adapted for stripping vaporizable material from a liquidwhich tends to foam during normal stripping operation which comprises aplurality of sequentially adjacent and interconnected chambers withterminal chambers at upper and lower ends thereof, each of the chambersincluding an outlet near the bottom thereof for removal from the chamberof the liquid being rectified, an inlet for admission to the chamber ofliquid-vapor mixture, an outlet near the top for removal from thechamber of vapor, said liquid-vapor inlet of each chamber being abovesaid liquid outlet and below said vapor outlet in said chamber, meansfor introducing feed to the stripping apparatus near the upper endthereof, means for withdrawing stripped product from the apparatus nearthe lower end thereof, means for adding steam or other stripping gasnear the lower end of the apparatus and means for withdrawing strippinggas or steam and material stripped from the feed, in gaseous or vaporform, near the upper end of the apparatus, the improvement whichcomprises: a first connecting walled passageway extending between thevapor outlet of the lower adjoining chamber and the said liquid-vaporinlet; a second connecting walled passageway extending between theliquid outlet of the higher adjoining chamber and an inlet to the saidfirst connecting passageway, with the proviso that the first passagewayin the lower chamber extends between a steam or stripping gas inlet andthe said vapor liquid inlet of the said lower terminal chamber and thesecond passageway is not present in the upper terminal chamber; saidsecond passageway includes a U-tube portion, the arms of which extendupwardly; the bottom of said U-tube being below the inlet to the firstpassageway; said inlet to the first passageway being adjacent to thevapor outlet of the lower adjoining chamber; and means for breaking foambeing present in at least some of the chambers.
 12. Apparatus as claimedin claim 11 wherein said first and second passageways are locatedexteriorly of said chamber.
 13. Apparatus as claimed in claim 11 whereinsaid means for breaking foam are provided in each chamber.